If you have never seen birds employing ants for pest control duties, you need to take a look at this fascinating clip. At first glance, it looks like a great example of a symbiotic relationship and even has its own name: ‘anting.’ We assume that both parties gain something from the arrangement. The birds get pesky bugs removed from their plumage, and the ants get a meal. However, the behavior is more complex than that, and there is still a lot that we don’t understand. Are the ants really willing participants in this behavior? What is its true purpose? Are there different types of this behavior? Let’s dive into the fascinating world of anting.
An Introduction to Anting
The term anting was first used by ornithologists in the 1930s to describe a behavior where birds applied ants to their plumage. These days, the scientific definition of anting is “the deliberate application of ants and ant secretions (or other pungent substances) by birds to their plumage or skin.” Therefore, the term is also sometimes used when birds apply other objects or substances, including citrus fruits and burning cigarettes, to their bodies.
This type of behavior is rarely seen in animals, yet it has been recorded in at least 200 avian species. Many of the birds that have been observed anting are songbirds. Some of the birds displaying anting behavior are the wood thrush, the northern cardinal, the house sparrow, the American crow, and the common raven.
Different Types of Anting
There are two main types of anting, called active (or direct) and passive (or indirect). However, the boundaries between the two types are not clear-cut. Some bird species practice both methods. Others, including the ravens (Corvus), combine both in one procedure. And a few bird species even combine both behaviors, creating a third ‘intermediate’ type of anting. There are no hard and fast rules regarding anting. Some birds do it every few days, but others only once in several years.
Active Anting
Ravens have been seen anting.
©iStock.com/wrangel
This is the most commonly observed anting behavior. During active anting, the ants are grasped in the bill and directly rubbed onto the feathers. A variation of this is to apply the ant to different parts of the feather and hold it there for a few minutes. This generally takes place on the ground or on a roost site such as a branch. The most common application site is the lower surface of the wing feathers. Sometimes the birds also spin in place, and the tail is usually rolled under the body and between the legs. Often the bird falls over!
Some, but by no means all, species go on to smear the ants over other body areas such as tail coverts and the feathers around the vent. This is most often seen in Corvidae, Icteridae, and Dicruridae.
Typically, only one ant is selected at a time and is either first smashed against a surface or used intact. It is then used for just one application, but some birds use them up to three times. A few bird species always grasp the ants in a certain way. For example, the blue jay holds their ants at the thorax, leaving the abdomen free. In a variation of this technique, some species use several ants at the same time or even a ball of crushed ants. Starlings often use a full bill of ants!
The whole procedure usually takes up to half an hour, but hour-long anting procedures have been recorded: they include some short breaks. It can be done alone or as part of a group.
Active Anting Substitutes
Not all active anting behavior involves ants! Birds will use plenty of so-called ant substitutes. Some invertebrate animals used in place of ants include:
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garlic snails
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millipedes
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grasshoppers
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wasps
But it gets even more bizarre than that! Birds have been seen using loads of other objects for anting. Here are just a few:
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leaves
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flowers
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fruits
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walnut shells
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burning cigarettes and matches
Perhaps the most extraordinary example was a large thrush rubbing itself with mothballs that had been left out in a yard to repel skunks.
Passive Anting
In passive anting, a bird walks over to or hovers above an anthill and presses its tail and wings into the ants. In what appears to be an attempt to provoke the ants, the bird passes its bill and head along different parts of its plumage. If ants crawl onto their head, they are often energetically shaken off. This behavior has been observed in robins, ravens, common starlings, and the house sparrow.
An intermediate type of anting is seen in the jay, the common green magpie (Cissa chinensis), and the red-billed blue magpie (Urocissa erythrorhyncha). Once the bird has placed itself within a swarm of ants, it spreads, stretches forward, and quivers both wings at the same time, and rests back onto its tail to encourage the ants to crawl up its body. Periodically, it passes its bill along its feathers, which looks like active anting, but there are no ants in its bill.
Which Ants Are Recruited?
Some ants produce formic acid.
©iStock.com/Antrey
Mostly, the ants used for this behavior belong to the subfamily Formicinae. The genera Formica, Lasius, and Camponotus are seen most often. So, what do we know about this particular group of ants that may have led to them being recruited?
When defending their nest, all of these worker ants bite with their mandibles and spray a venom gland excretion. This is stored in a reservoir and is delivered through an acidopore at the end of the ant’s abdomen. The secretion is made up of between 50 and 65 percent formic acid combined with some free amino acids and short peptides (proteins). Some ant species can spray their acid for several inches. However, formic acid is not the whole story.
Some ants, such as Dorymyrmex pyramicus (found in South America) from the subfamily Dolichoderinae, can secrete a substance from their anal glands. This has a distinctive smell and is widely believed to act as a repellent. Birds have also been seen using these ants for anting. Nevertheless, the preference is clearly for ants that can produce formic acid. Interestingly, birds are seemingly able to distinguish between ants that have a functional sting and those that rely on secretions for defense and select only the former as anting recruits.
What Is the Function of Anting?
The obvious assumption is that these birds are using the ants (or the substances that they excrete) for pest control. However, scientists have yet to confirm its exact function, and there is still a lot that we have to learn. That said, there are several theories that we can consider:
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Pest control: Anting may help to remove some of the ectoparasites, arthropods, fungi, and bacteria that birds have living in their plumage that they would prefer to remove.
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Improved grooming: The behavior may increase saliva production when using the bill to clean feathers or may remove old grease.
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Vitamin D: Anting may increase vitamin-D-rich oil production, which can then be swallowed when grooming.
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Reduce irritation: Skin can get irritated during grooming, and anting may help to control this.
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Safer Nutrition: Eating ants that spray formic acid in your mouth is not the best idea. Anting may stimulate ants to get rid of these noxious substances, so it is more pleasant to eat them.
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It feels good. Perhaps the birds simply like the feeling of ants in their plumage. Some birds become euphoric during the behavior.
Of course, the true purpose could be a combination of several or even all of these factors. Nevertheless, the pest control hypothesis has been both most investigated and most widely accepted. The fact that all of the ‘substitutes’ used in anting have some sort of pungent odor supports this theory. For example, the millipedes used in anting produce pungent toxins. It may also be used as a preventative measure by birds who are not infested or only mildly infested. Studies have shown that formic acid acts as a tick deterrent. However, there is no clear evidence that it actually reduces ectoparasites on birds. It also has bactericidal and fungicidal properties, but generally at higher concentrations than in secretions produced by ants. Birds clearly know why they indulge in anting behavior, but we still have a lot to learn about it.
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